The overall objective of the research is to understand the development and maintenance of spatial behavior. The major focus is on studies with kittens where the type of visual experience is varied. The research will test the viability of the necessity of active commerce with the environment of perceptual development, as maintained by Held and Hein and their collaborators, and the "two visual system" hypothesis which holds that form perception is innate and spatial behavior is learned. Kittens will be kept in the dark and then exposed to the light under different conditions. Some will be allowed active commerce with the environment and others will be restrained so that they obtain patterned light exposure but cannot locomote or view their limbs. Controls will remain in the dark. The kittens will be tested after 4, 8 or 12 weeks of deprivation. The 4 week period assesses the necessity of movement produced stimulation for the development of depth discrimination; the longer periods test the role of activity in maintaining it. Some animals will have different visual experience with each eye (active commerce with the environment with one eye, passive exposure with the other). Pilot research with young kittens, which needs to be extended, would indicate that the use of a different method shows that passively exposed animals discriminate depth as well as the active ones. The research uses the visual cliff to assess depth discrimination and a variety of methods (such as coaxing the animal over the glass with or without an apparent depth; the measurement of heart- rate, etc.). Other research on species differences and stimulus parameters for depth discrimination is proposed. The series of experiments will clarify the importance of activity for the development and maintenance of depth perception, including some quantification of the effects. The experiments have implications for the study of the importance of activity for perception with such special populations as the retarded or the physically handicapped.